Polishing sheet and method of producing same

ABSTRACT

A polishing sheet is produced by preparing a woven cloth sheet with single fibers, fiber bundles obtained by tying a plurality of fibers together, or bundle groups obtained by tying together these fiber bundles and impregnating such a woven cloth sheet with a resin solution such that the fibers and/or fiber bundles are fixed together. A backing sheet may be used to attach such a polishing sheet. Sateen woven cloths with sateen number 3-15 are preferred.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a polishing sheet for polishing atarget object requiring a high degree of smoothness for its surface suchas semiconductor wafers, liquid crystal glass substrates, magnetic harddisk substrates and magnetic head substrates and a method of producingsuch a polishing sheet. The invention relates in particular to such asheet adapted for chemical mechanical polishing.

[0002] A chemical mechanical polishing (CMP) method is commonly carriedout for polishing a target object requiring a high degree of smoothnessfor its surface such as semiconductor wafers, liquid crystal glasssubstrates, magnetic hard disk substrates and magnetic head substrates.The CMP method is carried out by using a polishing liquid containing acomponent which reacts chemically with the target surface to bepolished. While the target surface is chemically etched or whilecomplexes and oxides are being formed on the target surface, the surfaceis abraded mechanically by free polishing particles contained in thepolishing liquid. The CMP method is known to have the advantage of beingable to accomplish a very fine polishing work and to make a surfacesmooth to a very high degree.

[0003] In the field of semiconductor devices, for example, the so-calledmulti-layer wiring technology is becoming important for increasing thedevice capacity. In this multi-layer wiring technology, the base layermust be made extremely flat. If the base layer is uneven withprotrusions and indentations, they result in step differences and thewires formed over a step difference are likely to be broken easily.Thus, the desired functions cannot be expected, and the CMP method isrelied upon in order to make smooth a wafer having a wiring pattern andan insulating film formed thereon.

[0004] As disclosed in Japanese Patent Publications Tokkai 8-3540 and10-88111, for example, a CMP method may be used to make a semiconductorwafer flat by supplying an alkaline polishing liquid with a component(such as a water solution of potassium hydroxide) which reactschemically with the film formed on the wafer surface onto a polishingpad attached to a rotary lapping plate and pressing the wafer onto thispad. Prior art examples of a polishing pad used for such a purposeinclude a pad having a foamed base having many very small holes on thesurface (such as foamed polyurethane pads IC-1000 produced by Rodel,Inc.) and a pad having a sheet of woven cloth comprising plastic fibersaffixed to an elastic sheet such as a rubber sheet (as disclosed inJapanese Patent Publication Tokkai 55-90263. These polishing pads wereused because the free polishing particles held in the very small surfaceholes of a foamed material or in spaces between the fibers of the wovencloth were believed to elastically act on the target surface such thatthe target surface can be polished to a high degree of smoothness.

[0005] Prior art polishing pads using a foamed material were produced byfoaming a mixture of at least two resin materials to form a foamed blockand slicing such a foamed block to a desired thickness but it wasdifficult to control the degree of foaming to be uniform throughout thebody of the foamed block. Thus, the produced pads were different in thenumber of holes per unit area of surface and elasticity and localvariations were also present even on each produced pad.

[0006] If such a prior art polishing pad using a foamed material isused, furthermore, the polishing surface becomes worn out locally or asa whole, becoming deformed as time passes such that it becomes incapableof polishing the target surface uniformly. Besides, the small holes onthe polishing surface become clogged with abrading particles and debrissuch that the polishing rate (the amount polished per unit time) becomeslower. Thus, the common practice is to carry out the so-called dressingprocess by using a sand plate or the like with hard particles such asdiamond particles imbedded to recondition the pad surface. The dressingprocess is not only time-consuming but also troublesome in that hardparticles such as diamond particles removed from the dressing toolbecome attached to the pad surface, causing unwanted scratches on thetarget surface to be made smooth.

[0007] If a prior art polishing pad with a woven cloth is used, thefibers on the woven cloth on the pad surface become displaced as timepasses and the pad becomes deformed such that it becomes impossible topolish the target surface uniformly. At the same time, it becomesdifficult to keep the free abrading particles on the pad surface and thepolishing rate is adversely affected.

SUMMARY OF THE INVENTION

[0008] In view of the above, it is an object of this invention toprovide a polishing sheet which will not become deformed as time goes byso as to remain capable of polishing a target surface evenly andsmoothly.

[0009] It is also an object of this invention to provide a method ofproducing such a polishing sheet.

[0010] A polishing sheet embodying this invention, with which the aboveand other objects can be accomplished, may be characterized ascomprising a woven cloth sheet of a fiber, a fiber bundle with aplurality of fibers bundled up together or a fiber bundle assembly witha plurality of such fiber bundles bundled up together and a resinmaterial fixing the fibers or fiber bundles of the cloth sheet. Such apolishing sheet of the present invention may preferably attached to thesurface of a backing sheet of a plastic, woven or non-woven cloth orfoamed material by using a resin adhesive of a known kind such asurethane, polyester or acryl resins. Woven cloths which may be used inthis invention include plain woven, twill woven and sateen woven cloths.

[0011] Sateen woven cloths may be used as examples of woven sheets. Ifthe sateen number is increased, the surface roughness of the targetobject can be made smaller and the polishing rate can also be increased.The sateen number is preferably in the range of 2-15 and more preferablyin the range of 3-15.

[0012] Woven sheets of this invention may comprise fibers of known kindsnot only for the purpose of polishing but also for general use. Fiberswith thickness equal to or less than 0.1 deniers are used for reducingthe surface roughness of the target object and to increase the rate ofpolishing. Polyester fibers of thickness equal to 0.1 deniers or smallerare preferably used.

[0013] Examples of resin for fixing the fibers or fiber bundles of awoven sheet include urethane resins, polyester resins and acryl resins.Urethane resins may preferably be used. The density of resin in theresin solution is preferably in the range of 0.1%-30%. The resinsolution of this invention is obtained by dissolving such a resinmaterial in water, alcohol or a water-based solvent such as an organicsolvent.

[0014] Polishing sheets of this invention as described above may beproduced by impregnating such a woven cloth as described above with aresin solution and then drying the woven cloth impregnated with theresin solution.

[0015] A target object is polished by causing a polishing liquid to bepresent between a polishing pad or a polishing tape made of a polishingsheet of this invention and the surface of the target object to bepolished and causing a relative motion between the target object and thepolishing pad or the polishing tape. A polishing liquid with a componentwhich chemically interacts appropriately with the surface of the targetobject is preferably selected for carrying out a chemical mechanicalpolishing process. The invention does not require whether the polishingliquid should or should not contain abrading particles.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1(a) is a sectional view of a polishing sheet with sateennumber 5 embodying this invention and FIG. 1(b) is a surface photographby a scanning electron microscope taken of another polishing sheet withsateen number 8 embodying this invention.

[0017]FIG. 2 is a side view of a polishing machine for rotary lappingtype of polishing.

[0018]FIG. 3 is a side view of a polishing machine for rotary head typeof polishing.

[0019]FIG. 4 is a side view of a polishing machine for belt type ofpolishing.

[0020]FIG. 5 is a side view of a polishing machine for drum type ofpolishing.

[0021]FIG. 6 is a side view of a polishing machine for tape type ofpolishing.

DETAILED DESCRIPTION OF THE INVENTION

[0022] FIGS. 1(a) and 1(b) show a polishing sheet 10 embodying thisinvention, characterized as comprising a sheet 12 having single fibers13, fiber bundles 13 with a plurality of fibers tied together andassemblies 13 of a plurality of fiber bundles each with a plurality offibers and a resin material 14 fixing these fibers 13 and these fiberbundles 13 together. In order to prevent displacement in a transversedirection while being used in a polishing process, the polishing sheet10 is affixed to the surface of a backing sheet 15 by using an adhesiveagent 16 of a known kind such as a urethane resin, a polyester resin oran acryl resins. Examples of material to be used for the backing sheet15 includes plastic sheets such as polyester, polypropylene orpolyethylene terephthalate sheets, woven cloth sheets, non-woven clothsheets and foamed sheets made of a foamed material such as foamedurethane.

[0023] As the woven cloth sheet 12, sateen woven fibers and fiberbundles 13 may be used. If the sateen number in this case is too small,the polishing rate becomes too small and the surface roughness of thetarget object after the polishing process becomes large. If the sateennumber is increased, the polishing rate becomes larger and the surfaceroughness of the polished target object becomes small but if the sateennumber is made too large, the polishing sheet becomes too easilydeformed. It is therefore preferred that the sateen number be equal to15 or less and more preferably in the range of 3-15. FIGS. 1(a) and 1(b)show examples where the sateen number is 5 and 8, respectively.

[0024] Examples of fibers 13 forming the woven cloth sheet 12 of thisinvention include one or more selected from synthetic fibers such asnylon, polyester, acryl, vinylon, vinyl polychloride, polyethylene,vinyliden, polyurethane, polychlal, rayon, polynosic, cupra, acetate,triacetate and promix and natural fibers such as carbon fibers, silk,wool, cotton and hemp. Fibers with thickness equal to or less than 0.1deniers are used in order to make the surface roughness of the targetobject small and the polishing rate high. Polyester fibers withthickness equal to or less than 0.1 deniers are preferred.

[0025] The resin solution to be impregnated in the woven cloth sheet 12is obtained by dissolving a known kind of urethane or polyester resin inwater. The density of resin in the resin solution is in the range of0.1%-30%. A urethane resin solution may preferably be used such that thefibers and fiber bundles of the woven cloth sheet 12 are fixed togetherby urethane resin 14.

[0026] The polishing sheet 10 as shown in FIGS. 1(a) and 1(b) isproduced by impregnating the woven cloth sheet 12 with a resin solutionand drying this woven cloth sheet 12 impregnated with the resin solutionsuch that the fibers and fiber bundles 13 of the woven cloth sheet 12become fixed together by a resin 14. Preferably it is then affixed tothe surface of a backing sheet 15 by means of an adhesive agent 16. Inthis process, the resin solution may be impregnated in the woven clothsheet 12 by using a spray or by submerging the woven cloth sheet 12 in atank containing the resin solution. The woven cloth sheet 12 may beaffixed to the backing sheet 15 without using the adhesive agent 16 butby pressing the woven cloth sheet 12 impregnated with the resin solutionagainst the surface of the backing sheet 15 and drying the resinsolution. Instead of using the adhesive agent 16, a double-facedadhesive tape of a known kind (not shown) may be used on the backingsheet 15.

[0027] The polishing of the surface of a target object is accomplishedby causing a polishing liquid to exist between a polishing pad or apolishing tape made of the polishing sheet 10 as shown in FIGS. 1(a) and1(b) and causing the polishing pad or the polishing tape and the targetobject to move with respect to each other.

[0028] Some of representative polishing processes using the polishingmethod of this invention will be explained next.

[0029] 1. Rotary Lapping Method

[0030] This is done, as shown in FIG. 2, by pasting a polishing pad 10made of a polishing sheet of this invention on a lapping plate D. Thetarget object 11 to be polished is adsorbed to a head H and while thelapping plate D and the head H are rotated as shown by arrows, apolishing liquid is supplied through a nozzle N onto the polishing pad10 on the lapping plate D and the target object 11 is pressed onto thepolishing pad 10 on the lapping plate D.

[0031] 2. Rotary Head Method

[0032] This is done, as shown in FIG. 3, by causing a target object 11such as a glass plate for liquid crystal to be held on a lapping plate Dby means of a holder S such as a frame. While a polishing liquid issupplied to the surface of this target object 11 through a nozzle N, ahead H to which the polishing pad 10 made of a polishing sheet of thisinvention is attached is pressed against it and caused to movehorizontally on a serpentine path on the surface of the target object11.

[0033] 3. Belt Polishing Method

[0034] This is done, as shown in FIG. 4, by causing a target object 11such as a semiconductor wafer to be adsorbed onto a head H. As the headH is rotated, a belt-shaped polishing pad 10 made of a polishing sheetof this invention is run in the direction shown by an arrow. A polishingliquid is supplied onto the surface of the polishing pad 10 through anozzle N, and the target object 11 adsorbed to the head H is pressedagainst the polishing pad 10 running over a platen P having an elasticmaterial (not shown) affixed to its surface.

[0035] 4. Drum Polishing Method

[0036] This is done, as shown in FIG. 5, by causing a target object 11such as a semiconductor wafer to be adsorbed onto a head H and rotatingthe head H as shown by an arrow while a drum C with the polishing pad 10made of a polishing sheet of this invention pasted around it is causedto rotate as shown by another arrow. A polishing liquid is supplied ontothe surface of the polishing pad 10 around the drum C and the targetobject 11 adsorbed to the head H is pressed against it.

[0037] 5. Tape Polishing Method

[0038] This is done, as shown in FIG. 6, by causing a target object 11such as a semiconductor wafer to be adsorbed onto a head H and rotatingthe head H as shown by a head while a polishing liquid is suppliedthrough a nozzle N onto the polishing tape 10 made of a polishing sheetof this invention sent out from a supply roller R1 in the direction ofanother arrow. The target object 11 adsorbed to the head H is pressedagainst the polishing tape 10 on a platen P having an elastic material(not shown) affixed to its surface. The polishing tape 10 issequentially rolled around by a take-up roller R2. The polishing tape 10may be moved either continuously or intermittently such that the motionis stopped while the target object 11 is being pushed onto the surfaceof the polishing tape 10.

[0039] In the method according to this invention, a known kind ofpolishing liquid used for polishing with free abrading particles may beused but those containing a component which chemically react with thesurface of the target object are preferred. This is because, asexplained above, the chemical mechanical polishing has the advantage ofbeing able to carry out a high degree of planarization. When a metal orglass is polished by the chemical mechanical polishing method, acidicsolutions, solutions containing an oxidant, solution containing achelating agent, or alkaline solutions such as those containingpotassium hydroxide solution or sodium hydroxide may be used.

[0040] Examples of abrading particles dispersed in the polishing liquidinclude known kinds such as particles of silica, cerium oxide, alumina,zirconia and diamond.

[0041] When the chemical mechanical polishing method is used, it doesnot matter whether abrading particles are used or not. If a polishingliquid containing abrading particles is used, the rate of polishingbecomes greater than if a polishing pad based on a foamed material isused. If a polishing liquid not containing abrading particles is used,the rate of polishing is about the same as if a polishing pad based on afoamed material is used.

[0042] The invention is described next by way of results of experiments.

TEST EXAMPLE 1

[0043] A woven cloth sheet was prepared by using fiber bundles of 12bundles each tying together 70 bundles of polyester fibers of thickness0.06 deniers as weft and with sateen number of 8 (as shown in FIG. 1(b))and was impregnated with a resin solution prepared by dissolvingurethane resin (concentration 10%) in water. The impregnated woven clothsheet was dried and then attached to the surface of a polyethyleneterephthalate (PET) sheet by using an acryl adhesive agent to produce apolishing sheet embodying this invention. This polishing sheet was cutto produce polishing pad of Test Example 1.

TEST EXAMPLE 2

[0044] A woven cloth sheet was prepared by using fiber bundles of 12bundles each tying together 70 bundles of polyester fibers of thickness0.06 deniers both as weft and warp and with sateen number of 5 (as shownin FIG. 1(a)) and was impregnated with the same resin solution preparedin Test Example 1. The impregnated woven cloth sheet was dried and thenattached to the surface of a PET sheet by using a double-sided acryladhesive tape to produce a polishing sheet embodying this invention.This polishing sheet was cut to produce polishing pad of Test Example 2.

TEST EXAMPLE 3

[0045] A plain woven cloth sheet was prepared by using fiber bundles of12 bundles each tying together 70 bundles of polyester fibers ofthickness 0.06 deniers both as weft and warp and with sateen number of 2and was impregnated with the same resin solution prepared in TestExample 1. The impregnated woven cloth sheet was dried and then attachedto the surface of a PET sheet by using a double-sided acryl adhesivetape to produce a polishing sheet embodying this invention. Thispolishing sheet was cut to produce polishing pad of Test Example 3.

TEST EXAMPLE 4

[0046] A woven cloth sheet was prepared by using fiber bundles of 12bundles each tying together 70 bundles of polyester fibers of thickness0.06 deniers both as weft and warp and with sateen number of 3 and wasimpregnated with the same resin solution prepared in Test Example 1. Theimpregnated woven cloth sheet was dried and then attached to the surfaceof a PET sheet by using a double-sided acryl adhesive tape to produce apolishing sheet embodying this invention. This polishing sheet was cutto produce polishing pad of Test Example 3.

COMPARISON EXAMPLE 1

[0047] A woven cloth sheet was prepared by using fiber bundles of 12bundles each tying together 70 bundles of polyester fibers of thickness0.06 deniers both as weft and warp and with sateen number of 3 and wasattached to the surface of a PET sheet by using a double-sided acryladhesive tape to produce a polishing sheet. This polishing sheet was cutto produce polishing pad of Comparison Example 1.

COMPARISON EXAMPLE 2

[0048] This was a commercially available foamed polyurethane pad(IC-1000 produced by Rodel, Inc.)

COMPARISON EXAMPLE 3

[0049] A plain woven cloth sheet was prepared by using fiber bundles of34 bundles each tying polyester fibers of thickness 1.18 deniers both asweft and warp and with sateen number of 2 and was impregnated with thesame resin solution prepared in Test Example 1. The impregnated wovencloth sheet was dried and then attached to the surface of a PET sheet byusing a double-sided acryl adhesive tape to produce a polishing pad ofComparison Example 3.

[0050] Test 1

[0051] In this test, the effects of sateen number on the polishing rateand the surface roughness of a target object were examined by usingpolishing pads made of polishing sheets of Test Examples 1, 2 and 3embodying this invention (with sateen numbers 8 (as shown in FIG. 1(b)),5 (as shown in FIGS. 1(a)) and 2) produced by preparing sateen-wovencloth sheets with fiber bundles fixed with a resin and affixing themonto a backing sheet. In this test, target objects were 8-inch siliconwafers having a Cu film of thickness 8000 Å formed thereon byspattering. They were polished by using Polishing Liquid A shown inTable 2 below, containing alumina particles with average particlediameter of 0.1 μm, and a polishing machine of the rotary lapping type(Mechpol E550 produced by Pesi Co., Ltd.) as shown in FIG. 2, under theconditions shown in Table 1. TABLE 1 Polishing Conditions Rate ofrotation of head 40 rpm Rate of rotation of lapping plate 40 rpm Supplyrate of polishing liquid 250 ml/minute Pressure of compression 300 g/cm²Polishing time 60 sec

[0052] TABLE 2 Polishing Liquid A (for Test 1) Quinaldinic acid 0.67weight % Hydrogen peroxide water 4.67 weight % Lactic acid 1.33 weight %Alumina (average diameter 0.1 μm) 4.99 weight % Pure water 89.33 weight% 

[0053] The rate of polishing (in units of Å/minute) was determined byusing a 4-probe contact type resistance sensor for measurement of filmthickness to measure the abraded film thickness per unit time. Surfaceroughness (in units of Å) was measured by using a white colorinterference type surface roughness sensor (NEW VIEW produced by ZygoCo., Ltd.)

[0054] Results of the test are shown in Table 3, showing that the rateof polishing increases and the surface roughness of the target objectbecomes smaller after the polishing as the sateen number is increased.TABLE 3 Surface Rate of Sateen roughness polishing Number (Å) (Å/minute)Test Example 1 8 4.23 4027.2 Test Example 2 5 5.80 2626.9 Test Example 31 80.2 1779.6

[0055] Test 2

[0056] Polishing pads from Test Example 4 and Comparison Examples 1 and2 were used to polish wafers of the same kind as used in Test 1.Polishing Liquid A as used in Test 1 and Polishing Liquid B notcontaining abrading particles as described in Table 4 were used. It isto be noted that Polishing Liquid B contains the same components thatreact chemically with the Cu film to form complexes on the surface asdoes Polishing Liquid A. The same sensors were used for the measurementsof film thickness and rate of polishing and under the conditionsdescribed in Table 1 above. TABLE 4 Polishing Liquid B (for Test 2)Quinaldinic acid 0.67 weight % Hydrogen peroxide water 4.67 weight %Lactic acid 1.33 weight % Pure water 93.33 weight % 

[0057] Results of the tests are shown in Table 5. It shows that if apolishing pad of Test Example 4 is used, the rate of polishing isgreater than if a pad of Comparison Example 1 or 2 is used, whether ornot Polishing Liquid A or B is used. The surface roughness was equallygood (about 3.0 Å—about 4.0 Å) whether a pad of Test Example 4 was usedor a pad of Comparison Example 1 or 2 was used but it was found that thesurface of the wafer with Cu film as a whole was much more uniformlysmooth if a pad of Test Example 4 was used than if a pad of ComparisonExample 1 or 2 was used. TABLE 5 Polishing rate (nm/minute) TestComparison Comparison Example 4 Example 1 Example 2 Polishing Liquid A2136 1950 1300 Polishing Liquid B 1606 986 1290

[0058] Test 3

[0059] Polishing pads from Test Example 3 (with fibers of thickness 0.06deniers) and Comparison Example 3 (with fibers of thickness 1.18deniers) were used to polish wafers of the same kind as used in Test 1.Polishing Liquid A containing alumina particles with average diameter of0.1 μm shown in Table 2 was used, and the polishing was done by usingthe same polishing machined and under the same conditions as in Test 1.The rates of polishing and the surface roughness of the target objectswere examined as in Test 1.

[0060] Results of the test are shown in Table 6. The results show thatboth the rate of polishing and the surface roughness improve if thethickness of the fibers is reduced such that a flatter surface can beobtained in a shorter time. TABLE 6 Fiber Surface Rate of Sateenthickness roughness polishing number (denier) (Å) (Å/minute) TestExample 3 1 0.06 80.2 1779.6 Comparison 1 1.18 513.4 1680.5 Example 3

[0061] According to the present invention, the shape of the polishingsheet is stabilized and is not easily deformed. Thus, the target surfacecan be polished smoothly at a high rate of polishing even without theuse of abrading particles.

What is claimed is:
 1. A polishing sheet comprising: a woven cloth sheetwith single fibers, fiber bundles obtained by tying a plurality offibers together, or bundle groups obtained by tying together said fiberbundles; and a resin fixing said fibers or said fiber bundles together.2. The polishing sheet of claim 1 wherein said woven cloth sheet has asateen number in the range of 2-15.
 3. The polishing sheet of claim 1wherein said woven cloth sheet has a sateen number in the range of 3-15.4. The polishing sheet of claim 1 wherein said fibers are of thickness0.1 deniers or less.
 5. The polishing sheet of claim 1 furthercomprising a backing sheet having a surface, on which said woven clothsheet is affixed.
 6. A method of producing a polishing sheet, saidmethod comprising the steps of: impregnating with a resin solution awoven cloth sheet with single fibers, fiber bundles obtained by tying aplurality of fibers together, or bundle groups obtained by tyingtogether said fiber bundles; drying said woven cloth sheet impregnatedwith said resin solution and thereby fixing said fibers or said fiberbundles together.
 7. The method of claim 6 further comprising the stepof attaching said dried woven cloth sheet on a surface of a backingsheet.
 8. A method of polishing a surface of a target object to bepolished, said method comprising the steps of: preparing a polishing pador a polishing tape from a polishing sheet which comprises a woven clothsheet with single fibers, fiber bundles obtained by tying a plurality offibers together, or bundle groups obtained by tying together said fiberbundles and a resin fixing said fibers or said fiber bundles together;causing a polishing liquid to be present between said polishing pad orpolishing tape and said surface, said polishing liquid containing acomponent which reacts chemically with said target surface; and causingsaid polishing pad or polishing tape and said target object to move withrespect to each other.
 9. The method of claim 8 wherein said woven clothsheet is sateen woven with sateen number 1-15.
 10. The method of claim 8wherein said woven cloth sheet is sateen woven with sateen number 3-15.11. The method of claim 8 wherein said fibers are of thickness 0.1deniers or less.
 12. The method of claim 8 wherein said polishing sheetfurther comprises a backing sheet on which said woven cloth sheet isaffixed.